Welding apparatus



April 12, 1949. c LEATHERS 2,467,321

WELDING APPARATUS Filed Feb. 19, 1945 6 Sheets-Sheet l INVENTOR. ie'szef' April 12, 1949. c. F. LEATHERS WELDING APPARATUS 6 Sheets-Sheet 2Filed Feb. 19, 1945 INVENTOR. }eJz e/ ZX'eaii b.

BY v

April 12, 1949. c. F. LEATHERS 2,467,321

. WELDING APPARATUS Filed Feb. 19, 1945 6 Sheets-Sheet 5 1 akai/ev elecfaJes l I We [(4-1- 6233c: fins-Z INVENTOR.

C'gesze r Wed ie/a.

April 12, 1949. c. F. LEAT HERS WELDING APPARATUS 6 Sheets-Sheet 6Filed. Feb. 19, 1945 INVENTOR. f zr if'leqiZrers.

BY mgal zY/l kl.

Patented Apr. 12, 1949 UNITED STATES PATENT OFFICE WELDING APPARATUSCheater r. Leathers, Detroit, Mich. Application February 19, 1945,Serial No. 580,262

The present invention relates to resistance welding or heating systems,and is particular y directed to the provision of an improved multiplespot welder utilizing storage batteries as a source of welding energy.In certain of its aspects, the present invention is directed toimprovements upon the inventions disclosed and claimed in the copendingapplication of Fred H. Johnson and the present applicant, Serial No.479,998, filed March 22, 1943, now Patent 2,452,573, dated November 2,1948, and in the copending application of the present applicant, SerialNo. 435,322, filed July 17, 1944, now Patent Number 2,357,263, datedAugust 29, 944.

Principal objects of the present invention are to provide an improvedsystem of the above generally indicated type, which is simple inarrangement, economical of manufacture and assembly, efllcient andreliable in operation, and which is simple and inexpensive to maintain;to provide such a system embodying one or more storage battery units asa source of welding energy. and embodying improved means for selectivelyconmeeting the source to the diiferent groups of welding electrodes,each such rality of welding electrodes;

all of the groups of electrodes, and employing additional contactormechanisms which correspond respectively to different groups, theinitiation and termination of each welding operation being accomplishedby the action of the main contactor, and the selection of the group ofelectrodes which is to receive welding current, being accomplished bythe secondary contactors; and to generally improve multiple spot weldersof the battery operated type.

. able electrode assemblies;

5 Claims. (01. 171-97) 2 I Fig. 5 is a diagrammatic view in perspectiveshowing certain of the electrical and fluid circuits employed with themachine of Fig. 1.

Fig. 6 is a view in section of an illustrative main contactorconstruction;

Fig. 7 is a diagrammatic showing of a control system that may be usedwith the system of Figs. 1 through 6;

Fig. 8 is a diagrammatic view of a modification of the invention,illustrating its adaptability to different types of welding guns; and

Fig. 9 is a view showing one of the guns and one of the secondarycohtactors employed in the system of Fig. 8.

Referring first to the embodiment of Figures 1 through 7, theillustrative welding system comprises a multiple spot welding machine,or welder 20, and a self-contained power pack or source of weldingenergy 22. Except in respects noted hereinafter, the welder 20 may be ofgenerally conventional construction.

As shown, welder 29 comprises a base structure 24, which supports aseries of four columns 26. Columns 26 are surmounted by cover structure28, and serve as slidable guides for a work supporting table 30. Moreparticularly, sleeves 32 are secured to the underside of table 30, andthese sleeves are slidable upon the'columns 26. The table 39 normallyoccupies a lower position in which the fixed and movable Y trodes,described below, are relatively widely separated so as to facilitate theinsertion and removal of work into and from the machine; but may bemoved to an elevated position by means of a pair of spaced rams 34, thecylinders whereof are carried by the base 24, and the piston rods 36whereof are connected to the table 30. Rams 34 may be operated by eitherhydraulic fluid such as oil, or an elastic fluid such as air. In orderto positively hold the table 36 in its elevated position, it ispreferred to provide toggle mechanism, which is shown as embody a fluidpressure operated ram. The cylinder of this ram may be connected to, forexample, the arm portion 46, while the piston rod of this ram may beconnected to or may comprise the arm portion 48. As will be understood,a shortening of the link 44 breaks the toggle, enabling the table 30 tobe lowered. When the table 30 is elevated to its illustrated position,by means of the rams 34, link 44 may be extended so as to straighten thetoggle and enable the pairs of links 38-40 to positively support thetable in the illustrative upper orwelding position. In the latterposition, the fixed and movable welding electrodes may be only slightlyspaced apart or, and preferably, may be lightly engaged with each other.

As shown, table 30 forms a support for a bus bar 50, formed of goodconductive material, such as copper, or an alloy thereof, and which busbar is common to all of a plurality of relatively movable electrodes'52, which movable electrodes 52 are divided into'different groups, asis described in more detail in connection with Figure 4. Bus bar 50 isinsulated from table 30 in conventional fashion, as by means of theinterposed insulating material 54. Bus bar 50 is also integrally, orotherwise rigidly, connected to a cooperating bus bar 55, which, as isdescribed in connection with Figure 5, extends through a currentregulating rheostat mechanism, to one terminal of the power pack 22.

The top structure 20 forms a rigid support for two pairs oflongitudinally spaced downwardly projecting supporting brackets 60, oneof which is shown in Figure 1, and all of which are fragmentarily shownin Figure 5. These brackets 50 form supports for, and are insulatedfrom, corresponding bus bar sections 62 and 54. In the preferredpractice of the present invention there is one such bus bar sectionwhich is individual to each group of welding guns, but which is commonto all guns in a particular group. By way of illustration, the presentwelder is illustrated as being arranged to accommodate two groups andconsequently only two bus bar sections B2-64 are shown. As isdiagrammatically shown in Figure 5, bus bar sections 62 and 64 areeachprovided with lateral extensions 66 and 68 respectively, which areadapted to be selectively connected, by means of the hereinafterdescribed secondary contactors I and II, to the laterally extendingportions I2 and 14 of a cooperating bus bar section 16. The terminal 18of bus bar section 16 is rigidly secured by means of a usual flexibleconductor section 80, to one terminal 82 of the hereinafter describedmain contactor 84. The other terminal 80 of this contactor is connectedto the remaining terminal of the power pack 22.

The welding guns of the two groups are designated, respectively, as-90aand 90b, there being six guns in each group, although it will beunderstood that in practice each group may contain a different number ofguns, depending upon the capacity of the power pack and dependingfurther upon the current requirements of the individual welds which aremade by the guns of the individual groups.

Each gun, as clearly appears in Figure 4, comprises a cylinder I00,which is rigidly secured to the upper surface of a correspondingauxiliary bus bar section I02. Each cylinder I00 is closed at its upperend by means of a fitting I04, which accommodates a fluid supply lineI08. As shown in Figure 5, the lines I06 are common to and are connectedto a manifold I08, which is described hereinafter, serves as a source ofsupply to the actuating fluid, which is preferably oil. Each cylinderI00 slidably receives a piston IIO, the piston rod II2 whereof freelypasses through the corresponding auxiliary bus bar I02 and carries, atits lower end, a threaded enlarged portion H4. The corresponding movableelectrode H6 is threaded on to the extension &

ill and, in cooperation with an associated nut H8, serves to clampinglyengage a flexible shunt I20, the respective ends whereof are secured tothe bus bar I02 by stud I22 and I24. Each cylinder I00 is provided witha spacing sleeve I28 which limits the downward movement of theassociated piston M0, and consequently of the associated electrode 52.Sleeve I28 is preferably so adjusted that when the work W is applied tothe electrode 50, the upward movement of the table 30 brings the workinto engagement with the point 52 and elevates the latter toapproximately the position shown in Figure 4. At the time the table 30is elevated, pressure is relieved from the line I06, so that suchelevating move.- ment of the point 52 does not involve the applicationof any substantial pressure between electrodes 50-52 and the work.

Each auxiliary bus bar I22 is rigidly secured to the correspondingsecondary bus bar 52 or 64, it being appreciated that the individual busbar I02 and the corresponding shunts I20, as well as the remaining busbar features are so adjusted with respect to the current requirements ofeach weld and the resistance at each weld point, that the over allresistance of each branch welding circuit in each group is such thatwhen the welding circuit is energized, each weld receives the desiredquantity of current. These adjustments are, of course, determined by thecharacter of the work, the thicknessof the workpieces, and relatedwell-known factors. It will be understood, too, that the bus barsections .are such that as large a proportion as is reasonably possibleof the total resistance of each welding circuit is represented by theresistance at the junction between the workpieces.

Referring now to Figures 1 and 2, the battery unit or power pack 22 isillustrated as embodying the general construction described in moredetail in the aforesaid copending application, Serial No. 435,322. Moreparticularly, this unit comprises a generally rectangular framestructure which is defined by corner posts I30, cross members I32, and abase I34. The frame structure is-provided with removable doors I35, ateach side thereof, which doors may be provided with ventilating grillsI38. The frame structure also supports a plurality of shelves I40 whichindividually support the corresponding cells b which comprise thebattery u'nit. As will be appreciated, these individual cells may bearranged in various series, series-parallel, and parallel combinations,in accordance with the relative voltage and current requirement of theassociated welding circuits. Intermediate bus bar connections betweenthe individual cells are indicated at I48, all such connections of onepolarity being electrically connected to a common bus bar I48 which isrigidly connected to the previously mentioned terminal 86 of -the'maincontactor 84. The other terminal, for example, the negative terminal ofthe cell assembly is permanently connected to a vertically extending busbar I50 which isrigidly supported at the side of the machine which isopposite the bus bar I48. As is diagrammatically shown in Figure 5, busbar I50 lies between the legs of a heavy U- shaped conductor I52 whichhas a resistance which is relatively higher than that of bus bar I50.For example, member I52 may be formed I59 to an upwardly directedterminal portion I59 in the welding circuit.

Referring now particularly to Figure 5, the

contactor 94 is illustrated disks I and I12 which are replaceablyattached to cooperating supports I14 and I19. Support I15 is rigidlyconnected to, but is insulated from, the contactor base I19, by aplurality of circumferentially distributed studs I90. Support I14 inturn is rigidly secured to but is insulated from a cooperating pressureapplying member I92 by means of a plurality of circumferentialiydistributed studs I94. A plurality of circumferentially spacedcompression springs I99, the effect whereof may be varied by adjustingstuds I99, act between the support I14 and the base I19, andcontinuously urge such support and the upper disk I10 to a position invertically spaced relation to the lower carbon I 12. A limit to suchupward movement is aiforded by the engagement between associatedcylinder I94.

The cylinder I94 is rigidly secured to the top of a cooperating housingmember I95, and members I94 and I99 are supported in vertically spacedrelation to the base I19 by a plurality of posts I99 and spacers 290.The housing I95 actrunnions 204. The upper end of each lever 202 carriesa periphery grooved roller 205 which cooperates with a cam 209 which iscarried by the piston I90. The other arm of each bell crank is providedwith a recess or pocket 2I0 which accommodates a pressure pin 2I2 whichbears against the Piston I90 is continuously vated position by means ofcompression spring 2 which is seated between the piston and the base 2I5of the housing I99.

' rounds a post 2I9 which is fixed to the piston and is guided in asleeved opening 220 in the base 2I9.

In operation, the parts normally occupy a position in which thecarbonsI10 and I12 are spaced apart as aforesaid. To close the contactor, anactuating fluid, such as air, is admitted to the chamber space 222,thereby forcing piston I99 downwardly against the action of springs 2 I4and I99. This downward movement of the piston causes a rocking movementof the bell cranks 292 and a consequent downward movement of the supportI14 and its carbon I19. After the carbons I10 and I12 engage each other,thereby initially completing the circuit through the contactor, thepressure continues to build up in chamber 222, thereby increasing thepressure between the carbons and decreasing the resistance at thejunction therebetween. Thi decrease causes the welding current to risefrom an initial value to a maximum value. To open the contactor, the

pressure member urged to its elewelding current 8 space above piston I99is connected .to exhaust enabled to escape from the at a controlledrate. The reduction in pressure acting against piston I99 progressivelyreduces the pressure between the carbons and ultimately enables springsI99 to separate the carbons, interrupting the circuit throughthefcontactor. The rate of carbon-pressure decrease is preferably sorelated to the charwelding circuit as to cause the to fall to a valuewhich is a minor fraction of its maximum value, before the carbonsseparate.

Referring now to Figure 3, one of the previously mentioned secondarycontactors 10, H, 19, 15, and 11 is shown in detail. It will beappreciated that all of these contactors may be idenconnected to thecooperating two bus bar sections 59 and 14, by studs 232. Insulationsuch as 234 is interposed in the just-mentioned connections,

bus bars 99 and 14. The piston rod 235 is rigidly connected to the base230 and projects freely through the space between the bus bars 14 and59. Piston rod 235 is connected to a piston 239 which is slidablyreceived in an associated cylinder 240. A spring 242 surrounds thepiston rod and continuously urges the cylinder 240 to a position inwhich it is spaced from the bus bars 14 and 59. A supply line 244 for anactuating fluid, preferably oil, is connected to the end of the pistonrod so that actuating fluid can be admitted to the piston rod passage245 into the chamber space 249. inder to bodily move along the rod and,by engaging the bus bars 59 and 14, to complete an (0 electrical circuittherebetween.

It will be appreciated that the entire secondary contactor assembly isentirely supported by the associated bus bars. Opening and closingmovements of the secondary contactors therefore do not stress or tend tobend or distort these bus Separate mounting-means for the secondarycontactors are also dispensed with.

The supply lines 244 associated with the respective secondary contactors(Figure 5) lead. through associated individually operable two-way valves250, 252, 254, 255, and 259, to a conven tional pneumatic-hydraulicbooster 250 which may and preferably does embody the constructiondescribed in Martin Patent No. 2,126,490, granted August 9, 1938.Briefly, this booster comprises a relatively small hydraulic cylinder252, which receives a piston element 254, which in turn is connected toa larger piston 255, which ismovable in a cylinder 2991 Cylinder 299 ismounted upon a member 210 which serves as a reservoir for the cylinder252. An elastic fluid such as air can be admitted to the space abovepiston 299, through line 212, which controlled by a usualelectromagnetically operated three-way valve 214. When actuated, booster259 actuates one or the other, or both, of the secondary contactors 19and 1I,.depending upon the condition of valves 250 and 252. Thecondition of the secondary contactors 10 and H determines which of thegroups of welding guns 99a or b receives welding. current in response toclosure of the main contactor 94.

The actuation of the booster 299 also actuates one oi the currentcontrolling secondary contactors 19, 15, and 11, depending upon theconditions 7 of the valves 254, 250, and 258. As described above,secondary contactors l3, 15, and 11 determine what proportion of therelatively high resistance bus bar I52 is included in theweldin circuitand consequently'determine the magnitude of the current delivered to theactive group or groups of welding guns.

'llhe manifold I08, which serves as a source of supply for theindividual welding .guns is connected, through a line 280, with abooster 282' which may and preferably does duplicate the booster 280.Booster 282 is supplied through a line 284, under control of a usualelectromagnetically operated three-way valve 286. It will be appreciatedthat when valve 286 is opened to admit air to the booster 282, thehydraulic piston 288 thereof forces oil through the line 280 and thencethrough the manifold I08 and the individual lines I08 into all of thewelding guns 90a and 80!), thereby causing the corresponding movableelectrodes to engage the work with a pressure suitable for welding. Itis preferred to thus apply pressure to all of the electrodes at the sametime, It will be appreciated that in the broader aspects of theinvention any of a wide variety of control systems may be utilized toprovide for the proper operation of the main and secondary contactorsand so as to insure the delivery of the proper amounts of weldingcurrent to the individual groups of electrodes. An illustrative controlsystem is diagrammatically shown in Figure 7, in which the propersequencing of the control valves referred to above is effected byutilizing a conventional weld timer 300 of the so-called pulsation type,and an indexing unit 302 of the electromagnetically controlled ratchettype. Timer 300 may be entirely conventional in arrangement and isconsequently shown in outline only, it being understood that this timermay be energized by momentarily closing the illustrative pilot switch P.When so energized, the timer establishes an over-all welding period,during which all of the groups of electrodes are maintained inengagement with the work at the welding pressure, and during which thesegroups of electrodes are successively supplied with welding current. Asdiagrammatically shown, timer 300 includes a usual control relay CRI,having contacts designated a and b. Relay CRI closes in response toclosure of the pilot switch and remains closed until the completion ofthe welding period. Timer 300 also incorporates a control relay CR2which opens and closes an adjustably predetermihaable number of timesduring the welding period. This relay closes shortly after closure ofrelay CRI, and opens for the last time in the succession, shortly priorto the reopening of relay CR2. Relay CRI is provided with a set of threecontacts a, b, and c which openand close in the sequence indicated inthe legends.

The indexing unit 302 comprise a toothed ratchet wheel 304 which iscontinuously biased to the illustrated position by means of a spiralspring 308, but which can be advanced in step by step fashion by anadvancing pawl 308 which is connected to an armature actuated by the'solehold-3i 0. A holding pawl 3I2 serves to hold the ratchet wheel ineach of its successive advanced positions, but may be retracted topermit a return or resetting movement of the ratchet wheel, byenergizing-the associated solenoid 3l4-. The circuit for solenoid 3includes a limit switch ill, which is opened when the ratchet wheel isat its normal or reset position but is closed at all 8 other timm. Abattery 320 serves as an illustra tive source of power for solenoids 3I0and 8.

The indexing wheel 804 drives a pair of commutator anms 322 and 324which in the normal or reset position of the indexing unit, are out ofcooperation with associated contacts a, b, and 0, etc., and which aresuccessively moved into enagement with such contacts as the indexingunit advances. Contacts 0, b, and 0 associated with the commutator arms322 and 324 are selectively connectable through usual plug and Jackassemblies 328 and 328, to the previously mentioned valves associatedwith the current regulator I50-l52 and with the valves which serve toselect the groups of welding electrodes.

It is believed that the remaining details of the system of Figures 1through '7 may best be understood from a brief description of theoperation thereof.

Assuming it is desired to make a weld, the work may be introduced intothe space between the common bus bar 50 and individual welding points52. This is preferably done at-a time when the table 30 is in itslowered position, After such placement, rams 3444 may be actuated toelevate table 30 and lock it in its elevated position. The means foraccomplishing this, being conventional, are not shown. The elevatingmovement of the table 30 brings bus bar 50 and the work to a position inwhich the electrodes 52 are lightly engaged therewith.

Thereafter, pilot switch P may be closed, energizing the weld timer 300.I Such energlzation results in a prompt closure of control relay CRI,which thereupon closes its contact a and opens its contact I). Theopening of contact b is without effect since the circuit for ratchetreset solenoid 3I4 is now interrupted at limit switch 3I8. Closure ofcontact a of relay CRI completes an obvious energizing'circuit for thewinding (not shown) of the previously mentioned conventional three-wayvalve 288 associated with booster 282 (Figure 5). Upon being energized,valve 286 admits air to the booster 282, which thereupon applies asuillcient pressure to the oil in line 280, header I08, and theindividual lines I08 to cause all of the welding guns a and b to presstheir associated movable electrodes 52 into engagement with the work atthe welding pressure; This action serves to firmly locate the work inproper position for the welding operation.

At the expiration of an adjustable interval following closure of relayCRI, relay CR2 moves to the closed position. It will be understood thatthis interval may bea fixed interval, or it may be an interval which isdetermined by a usual pressure switch which responds to the pressure in,for example, the line 280. Upon being energized as aforesaid, relay CR2successively closes its contacts 0, b, and a. Closure of contact 0completes an energizing circuit for solenoid 3 I 0 which thereuponadvances pawl 3'08 and causes the ratchet wheel 304 to advance to aposition in which commutator arms 322 and 324 are in engagementrespectively with their associated terminals (1. Such commutatormovements complete obvious energizing circuits for the previouslymentioned valves 254 and 250. These'valves are of usual normally closedconstruction which are open when and so long as the associatedelectromagnets are energized. The opening of valve 250 (Figure 5connects booster 260 to secondary contactor 10 associated with the groupof welding guns 80a. The opening of valve 254 connects booster 280 tothe secondary contactor l3 associ- '9 ated with the current regulatorl50l52.- It will be noticed that as shown this secondary contactor is insuch a position that only a very small amount of the bus bar I52 isincluded in the welding circuit. The actuation or secondary contactor 13thus establishes a relatively low resistance welding circuit,appropriate to the delivery of a relatively high value of weldingcurrent to guns 90a;

Shortly after the above described actuations of secondary contactors and13, contacts b of relay CR2 close. completing an obvious energizingcircuit for valve 214 associated with booster 260. Upon being energized,valve 214 admits air to the booster 260, causing a delivery of oil fromcylinder 262, through the now open valves 250 and 254, into secondarycontactors I0 and 13, thereby causing these contactors to close andprepare the aforesaid selecting and current regulating circuits. 1

At the expiration of an interval following the actuation of booster 260,which is suificient to insure closure of contactor l0 and 13, contact aof relay CR2 closes, completing an obvious energizing circuit for valve85 associated with the main contactor 84. Upon being so energized, valve85 admits air to the chamber 222 associated with the main contactor 84(Figure 6) and causes the previously described closing and resistancedecreasing action thereof. This action initiates a flow of weldingcurrent from the battery unit 22 through contactor 84, bus bars 16 and62, the flex ble connectors I20 associated with the individual guns 90a,electrodes 52, the work, bus ars 50, 56, and l54,.a Portion of bus barI52, and bus bar I back to the battery unit.

At the expiration of the time interval established by timer 300, relayCRI resumes the illustrated open position, successively reopeningcontacts a, b, and c. The reopening of contact a deenergizes valve 85,thereby. causing the main contactor -84 to reopen, interrupting the flowof welding current. After a short interval suflicient to insure thecomplete-opening of contactor 84, contact I) of relay CR2 reopens,interrupting the circuit for valve 214 associated with booster 260. Thisaction relieves the hydraulic pressure applied to secondary contactorsables the associated return springs 242 (Figure 3) to open thesecontactors.

At the expiration of a short interval, suiiicient to permit the completeopening of the secondary contactors 10 and 13, contact c of relay CR2reopens deenergizing solenoid 3| 0 and enabling its associated spring 3to pull it back to a position in which it engages behind the nextsucceeding ratchet tooth, preparatory to the next indexing operation.

At the expiration of the oil period for relay CR2 determined by timer300, this relay recloses, duplicating the operations previouslydescribed with the exception that in this case the energization ofratchet solenoid 3| 0 causes the indexing unit to advance the commutatorarms 322 and 324 into engagement with the associated terminals b. Thisindexing movement deenergizes valves 250 and 254, permitting them toreelose; and energizes valves 252 and 256, associated respectively withsecondary contactors H and I5. It will be appreciated that the plug andjack connections 326 and 328 enable the control valves to be connectedto desired ones of the commutator terminals. For example, terminal b ofcommutator 322 may, if desired, be arranged to energize valve 258instead of valve 256. In Figure 5, as

10 and i3 and en-- booster 10 will be evident, valve 256 establishes ahigher value of welding current than does valve 258.

The remaining operations are the same as those described above, with theexception that in this case, the now closed contactor II causes thewelding current to be delivered to the group of welding guns b and valve256 establishes a somewhat lower value of welding current than wasestablished for welding guns 90a in the preceding operation.

In the present simplified showing, it is assumed that the same period ofcurrent flow is appropriate for both groups of guns 90a and 90b. Ifdesired, the indexing unit 302'may be provided with an additionalcommutator arm 330, the associated terminals a, 2), etc., whereof areassociated with the timer 300 periods for relay CR2 corresponding toeach position of the commutator. Such adjusting circuits being.conventional, are not shown.

In the present system also only two groups of welding guns 90a and 90bare illustrated. Consequently, timer 300 is set so as to limit thesuccessive on periods of relay CR2 to two such periods and the over allwelding period is set so as to cause relay CRI to resume thede-energized position shortly after the conclusion of the second "on"period for relay CR2.

Following the above described resettin operations which result from thede-energization of relay CR2 accordingly, relay CRi resumes thede-energized position, opening its contacts a and reclosing its contacts17. The reopening of contacts a de-energizes valve 286 associated with282, relieving the pressure on the electrodes 52. Reclosure of contactbof relay CRI completes an energizing circuit for solenoid 3i4 associatedwith the reset pawl 3i2. This action withdraws the reset pawl fromcooperative engagement with the ratchet teeth, enabling the returnspring 306 to promptly restore the ratchet wheel to its startingposition. When the starting position is reached, limit switch 3 I 8reopens, interrupting the reset circuit. During the return movement ofthe ratchet wheel, all associated commutator arms sweep back across allof the contacts which they have previously engaged. Such return sweepcompletes momentary energizing circuits for the associated valves andfor the elements associated with arm 330. Such energizing circuits are,however, without eiTect since all other parts of the system are now in anormal or de-energized condition.

The modified embodiment of the invention shown in Figures 8 and 9illustrate the adaptability of the invention to differing types ofworkpieces and to differing types of welding guns. Figures 8 and 9 alsoillustrate the use of a motor driven pump unit 350 as a source of powerfor actuating the various groups of welding guns, instead of the boosterunit 282 of Figure 5.

In Figures 8 and 9, three groups of welding guns 352a, 352b, and 3520are provided for. The bus bar arrangement accordingly includes a commonbus bar 354 and individual electrically separate bus bars 356, 350, and360. These individual bus bars are arranged to be selectively connectedby secondary contactors 10, l l, and H to a common bus bar 362 which isconnected, through the main contactor 84, and the regulator l50l52, toone terminal of the battery unit 22. The other common bus bar 354 isdirectly connected to the other terminal of the battery unit 22. It willbe understood that bus bar sections of respectively oppoin such relationas to establish on the points 312 to clamp the work W therebetween.

When such hydraulic pressure is released, points 312 are caused toseparate, either under the influence of a usual return spring (notshown) associated with the ram 380, or under the influence or theassociated flexible supporting bus bars 384 and 386, which as shown,constitute the sole means for supporting each associated gun upon theassociated bus bars 354 and 356. Each supply line 382 is connected to aheader 390 which in turn is connected to the pump The control systemdescribed in connection with Figures 1 through 6 may, of course, beutilized in connection with the operation of Figures 8 and 9 with theexception that contact a of relay CRI, instead of controlling a boostervalve 286, will be arranged to control the operation of the pump 35! soas to cause the closing and opening operations of the individual guns352a, etc.

It will be appreciated from the foregoing that the presentinventionprovides very flexible multiple spot welding systems which, inthe first instance, enable the energy from a single storage battery unitto be simultaneously delivered to a plurality of welding points, andenable successive flows of welding current to be delivered to suecessivegroups of guns. In practice, battery charging mechanism is usuallycontinuously connected to the battery unit, so that the energy in eachweld is derived in major part from the battery unit, and in minor partfrom the source. Energy taken from the battery unit during each weld isreturned thereto during the intervals between the welds. Since the majorpart of the energy for each weld is derived from the battery unit, thecurrent demand from the line associated with the charger is very light.Consequently, each gun of a group may be supplied with a relatively highvalue of welding current without imposing undue demands on the linesupplying the charger. This factor materially reduces power costs, andthe ability to make a plurality of welds similarly materially increasesproduction rates.

Although only several specific embodiments of the invention have beendescribed in detail, it will be appreciated that various furthermodifications in the form, number, and arrangement of the parts may bemade without departing from the Y tween said sections.

2. In a high amperage low voltage electrical system, a plurality 01energy using elements, each element being disposed to receive a pulse ofcurrent of predetermined magnitude, a source of unidirectionalsubstantially non-pulsating voltage common to said elements forsupplying low voltage high amperage current, circuit connectionsinterposed between said source and said elements and including a circuitportion common to said elements and a plurality of branch circuitportions which correspond respectively to said elements, and contactormechanism for controlling 'fiow of current from said source to saidelements,

said contactor mechanism including a contactor common to said elementsand interposed insaid common circuit portion, and a plurality ofcontactors individual respectively to said elements and interposedrespectively in the corresponding branch portion.

3. The systemoi claim 2 including means operable, in causing thetransmission of pulses of current through said elements, to first closethe individual contactor corresponding to a particular element and tothereafter close the common contactor.

4. In a high amperage low voltage'electrical system, a plurality ofgroups of energy using elements, each group containing a plurality ofelements and each element being disposed to transmit a pulse of currentof predetermined magnitude, a source of unidirectional substantiallynonpulsating voltage to said groups for supplying low voltage highamperage current, circuit connections interposed between said source andsaid elements and including a circuit portion common to said groups anda plurality of branch circuit portions which correspond respectively tosaid groups, and contactor mechanism for controlling flow of currentfrom said unit to said elements, said contactor mechanism including acontactor common to said elements and interposed in said common circuitportion, and a plurality of contactors individual respectively to saidelements 'and interposed respectively in the corresponding branchportion.

5. The system of claim 2 including means operable, in causing thetransmission of pulses of current through said groups, to first closethe individual contactor corresponding to a particular group and tothereafter close the common contactor.

CHESTER F. LEATHERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

